Difference between circuit theory and electromagnetic field theory

Circuit Theory: As the name suggests, circuit theory deals with electrical circuit. An engineer can predict the performance of complicated electrical networks with the help of circuit theory. But this theory has certain limitations like :

It cannot be applied in free space.

It is useful only at low frequencies.

This theory is unsuccessful in explaining the radiation of electromagnetic waves into space in radio communications.

It cannot be used to analyse or design a complete communication system. Example: Radio Communication System.

Electromagnetic Field Theory. Although electromagnetic Field Theory (EMFT) is complex in comparison with circuit theory but EMFT is simplified by using appropriate mathematics. This theory deals with E and H vectors, whereas circuit theory deals with voltages and currents.
This theory has following advantages in comparison to circuit theory:

It is also applicable in free space.

It is useful at all frequencies, particularly at high frequencies,

The radiation effect can be considered.

This theory can be used to analyse or design a complete communication system. Example: Wireless Communication, Radio Communication.

Reference: This article is referred from my authored book “concepts of electromagnetic field theory”. In case of any problem, please post in the comment section.